Historically, soils contaminated with the lighter fractions of petroleum hydrocarbons, such as, gasoline, diesel fuel, and light burner fuels, have not been considered to be a major environmental problem. As this perception has changed, a number of systems have been devised to solve this problem. However, such systems have suffered from a number of drawbacks among which are (1) moving, but not truly cleaning, the soil; (2) difficulty of implementation; (3) limited effectiveness; (4) high cost; (5) inability to use at smaller sites; or (6) creating air or water pollution in the process of cleaning the soil.
It is therefore proposed to provide for a method and apparatus for separating the lighter hydrocarbon distillates from soil and in such a way as to achieve an effective thermal treatment which fully cleans the soil and is cost-effective. At the same time, it is desirable that the apparatus be of compact size and relatively inexpensive to produce so as to make it conformable for use on small sites; and the method of treating the exhaust gas will make the system both less expensive to operate and less environmentally damaging than alternative technologies. For example, it is desirable to employ a baghouse or filtering unit to efficiently remove fines from the hot exhaust gas stream produced during combustion of the lighter fractions, but in the past a filtering unit has not been practical for use because of the danger of explosion of the exhaust gases in passing through the unit.
Representative of past systems and methods is U.S. Pat. No. 4,746,290 to S. G. DeCicco et al in which contaminated soil passes downwardly through an inclined dryer, and a burner is movably positioned at the lower end of the dryer having an adjustable vented area to regulate the amount of combustion air. The treated waste material is carried into a cooler and discharge conveyor while the off gas is advanced to a combustion unit having a holding section for the destruction of the unwanted organics. In U.S. Pat. No. 4,715,965 to A. L. Sigerson et al, a preheater and heat exchanger are used in combination to vaporize the contaminants in the soil passed therethrough and the vaporized constituents are then passed through filtration stages to remove any solids. In this process, the combustion gas is taken to a temperature on the order of 750.degree. F. to 1800.degree. F. Other representative patents of interest are U.S. Pat. Nos. 4,738,206 to J. W. Noland, 4,787,323 to G. L. Beer et al, 4,667,609 to R. Hardison et al, 4,576,572 to E. E. Mueller et al and 4,427,376 to R. E. Etnyre et al. Generally lacking in the foregoing and other systems that have been devised is a compact, efficient system which can be truck-mounted or otherwise transportable to intended sites in the treatment of contaminated soils and efficient removal and disposal of such contaminants.